This invention relates to improvements in advance mechanisms for advancing a ribbon in a printer, such as an ink ribbon in a dot-impact serial printer.
Generally, in a printer using an ink ribbon, a print head for printing on recording paper and the like often operates reciprocally and a mechanism is used for winding an ink ribbon in a ribbon cassette in one direction, using only a unidirectional driving force of. the driving force of the reciprocating print head.
The winding mechanism shown in FIG. 8 has been known. The winding mechanism comprises an arm 115 in contact with a gear 111 which converts the reciprocating operation of a print head into rotational motion. The arm 115 follows the gear 111 by friction. An idler gear 112, which engages with the gear 111, moves with the arm rotation.
When the print head is moved in one direction and the gear 111 is rotated clockwise, the arm 115 is also rotated following the gear, causing the idler gear 112 and the gear 114 to engage with each other, and thereby to drive a gear 113 coupled directly to a ribbon winding spool. Conversely, when the print head is moved in an opposite direction and the gear 111 is rotated counterclockwise, the arm 115 also is rotated following the gear, causing the idler gear 112 and the gear 114 to be disengaged.
However, the winding mechanism of FIG. 8 has the following problems: When the idler gear 112 and the gear 114 are placed out of engagement, namely, when the print head is moved in the direction in which an ink ribbon is not fed, the tension given to the ink ribbon is reduced and the ink ribbon becomes slack. If the movement direction of the print head is changed and the gear 113 coupled directly to the ribbon winding spool is driven, tension is again applied to the slack ink ribbon, but the ink ribbon is not advanced until it becomes tight following the initial stage of moving the print head. Therefore, the print head must make an extra movement until the ink ribbon is wound after the movement direction of the print head is changed, causing the print time of the print head to be prolonged as much as that time interval.
If the print head is moved with the ink ribbon slack, recording paper and the like can become dirty or the print head catches the ink ribbon. This is also a problem.
The invention is intended for solving such technical problems of the prior art. It is an object of the invention to provide a printer comprising an advance mechanism for advancing a ribbon while preventing the ribbon from becoming slack when a driving force is not applied.
It is another object of the invention to provide a printer for reducing the likelihood that recording paper and the like will become dirty or that the ribbon will be caught.
In one embodiment of the invention, a printer is provided comprising a dot-impact head for striking an ink ribbon for printing on recording paper, a carriage mounting the dot-impact head thereon, a motor, a carriage drive mechanism connected to the motor for reciprocating the carriage by turning the motor forward and in reverse, an advance mechanism or winding spool for advancing the ink ribbon in one direction, and a transfer mechanism connected to the carriage drive mechanism. The transfer mechanism transfers a driving force of the motor to the advance mechanism when the carriage is moved in a first direction and releases the driving force of the motor from the advance mechanism when the carriage is moved in a second direction opposite to the first direction.
The advance mechanism of this embodiment comprises a support shaft, a winding member rotatably supported on the support shaft and rotation limiter. The winding member winds the ink ribbon by rotating in a third direction. The rotation limiter is provided in the winding member, allows the winding member to rotate in the third direction and inhibits the winding member from rotating in a fourth direction opposite to the third direction.
The winding member is limited by the rotation limiter so as to rotate only in the ink ribbon winding direction, so that if a force acts on the winding member, which would loosen the ink ribbon in a state in which a driving force is not transferred to the winding member, the winding member is limited in rotation by the rotation limiter and does not rotate in the opposite direction to the winding direction (fourth direction), thus the ink ribbon does not become slack.
Consequently, when transfering a driving force to the winding member intermittently for winding the ink ribbon, winding of the ink ribbon can always be started at the state in which the ink ribbon is tight. That is, if the print head moves in the direction not winding the ink ribbon or a driving force is not transferred to the advance mechanism, the ink ribbon is always held in a state in which it is tight. Thus, when winding the ink ribbon is again started, it is possible to reduce the time required for making the transition of the ink ribbon from the loose state to the tensioned state and to reduce the movement distance of the print head. Since the ink ribbon is not slack, smudging of recording paper and the like caused by contact with the ink ribbon and catching the print head in the ink ribbon can be prevented.
In this invention, the concept of xe2x80x9cadvancingxe2x80x9d includes not only the generally assumed meaning of winding around a winding shaft, but also the meaning of circulating, for example, by feeding in one constant direction. More particularly, an embodiment of the mechanism can be configured as follows:
The transfer mechanism comprises a first gear connected to the carriage drive mechanism, a first gear shaft rotatably supporting the first gear, a lever pivotally supported on the first gear shaft and having an arc-shaped guide groove centered on the first gear shaft, a second gear connected to the advance mechanism, a second gear shaft rotatably supporting the second gear and engaging the guide groove for guiding the pivotal movement of the lever, a third gear shaft provided on the lever, and a third gear rotatably attached to the third gear shaft and engageable with the second gear. In this case, the lever may be adapted to move in a direction in which the third gear engages with the second gear when the carriage is moved in the first direction, and move in a direction in which the third gear disengages from the second gear when the carriage is moved in the second direction.
A rotation limiter can be used which comprises a first coil spring wound around the support shaft having one end part fixed to the winding member. In this case, the first coil spring is deformably attached to the support shaft so that the first coil spring tightens on the support shaft when the winding member is rotated in the fourth direction, and is loosened from the support shaft when the winding member is rotated in the third direction.
Accordingly, if the winding member is rotated in the opposite direction to the winding direction (fourth direction) with respect to the support shaft, the torsion spring (first coil spring) tightens on the support shaft, therefore rotation of the winding member in the opposite direction to the winding direction can be easily suppressed. Generally, the torsion spring has excellent durability concerning wear proof and is inexpensive, therefore an advance mechanism excellent in durability and cost efficiency can be provided. Since the torsion spring is accommodated in the winding member, it is shut off from external dust, and the like. Therefore, dust, and the like, can be prevented from entering the clearance between the torsion spring and the coil spring, avoiding wear of the torsion spring or the support shaft, and an advance mechanism having higher durability can be provided.
When a ribbon cassette containing an ink ribbon is mounted on the printer, a hole in the bottom of the ribbon winding roller on the ribbon cassette side engages a connection part formed at the tip of the winding member on the printer side, whereby the ink ribbon in the ribbon cassette is transported. The hole made in the bottom of the winding roller can be formed in its inner periphery with a spline (key groove). The winding member also can be formed on the outer periphery of the tip (connection part) with a spline corresponding to the spline made in the inner periphery of the hole.
In an embodiment of the invention, the tip of the winding member (connection part) can be configured as follows: The winding member comprises a fourth gear connected to the transfer mechanism, a base part comprising a bearing for receiving the support shaft, and a connection part attached to the base part so that it can be moved in a direction parallel to the support shaft. In this case, a second coil spring for urging the connection part in a direction away from the base part is placed in the base part. Further, an annular groove for fixing one end of the second coil spring may be formed in the outer section of the bearing. Thus, the connection part connected to the ribbon cassette is attached to the base part of the winding member so that it can be moved up and down, and is urged upward by the coil spring, so that when the ribbon cassette is mounted, if the splines of the hole and the connection part do not match, the connection part is moved to the base part side. Then, when the winding member is driven and both spline positions match, the connection part is pushed by the second coil spring and engages the hole on the ribbon cassette side. Such a configuration makes it possible to prevent the tip of the winding member from becoming broken. The annular groove for fixing one end of the second coil spring is formed in the outer part of the bearing, the first coil spring-which is the rotation limiter-is located below the bearing, and the second coil is located above the bearing, so that the advance mechanism can be miniaturized.